1. Field of the Invention
The present invention relates generally to lubricant compositions useful in medium speed diesel engines, such as commonly found in railroad locomotives, marine towboats and stationary power applications. These engines frequently have silver bearings which necessitate lubricant compositions incorporating specialized silver protective agents to protect against wear, extreme pressure and corrosion of silver parts. However, it is well known that zinc-containing wear agents such as zinc dihydrocarbyldithiophosphates (typically used in passenger cars) cannot be used for this purpose given their incompatibility with silver bearings. It is also desirable to find alternatives to chlorine containing silver lubricity agents widely used in the art for silver protection. Thus, the present invention, more particularly, is directed to a lubricating composition, preferably essentially free of zinc dihydrocarbyldithiophosphate compounds, and optionally free of chlorine containing silver lubricity agents, comprising a major proportion of an oil of lubricating viscosity and a minor amount of a silver protective agent comprising the reaction product of a C.sub.5 to C.sub.60 carboxylic acid and at least one amine selected from the group consisting of (1) guanidine, urea, and thiourea compounds; (2) C.sub.1 to C.sub.20 hydrocarbyl or hydroxy-substituted hydrocarbyl mono-amines, alkylene diamines, and (3) polyalkylene polyamines; and N-alkyl glycine. A preferred guanidine reactant is aminoguanidine, or its salts, such as, preferably, aminoguanidine bicarbonate; a preferred alkylene diamine reactant is ethylenediamine; and a preferred N-alkyl glycine is N-methyl glycine. Preferred carboxylic acid-amine reaction products based upon guanidine are the aminoguanidine fatty acid amides and the corresponding 1,2,4-triazole-3-amines, in particular, aminoguanidine monooleamide and oleyl-1H-1,2,4-triazole3-amine. Preferred carboxylic acid-amine reaction products using an alkylene diamine as the amine reactant are the fatty acid imidazolines. Preferred carboxylic acid-amine reaction products using N-alkyl glycine as the amine are the fatty acid amides of N-methyl glycine.
The invention is further directed to a method for protecting silver parts in an internal combustion engine by lubricating the same with a lubricant composition comprising a major proportion of an oil of lubricating viscosity and a minor amount of at least one of the above-mentioned silver protective additives.
In a further aspect of the invention, the above silver protective additives are found to work in synergy with organo-sulfur compounds, preferably thiadiazole compounds selected from the group consisting of
(a) 2,5-dimercapto-1,3,4-thiadiazoles, PA1 (b) 2-(mercapto)-5-(hydrocarbylthio)-1,3,4-thiadiazoles, PA1 (c) 2,5-bis-(hydrocarbylthio)-1,3,4-thiadiazoles, PA1 (d) 2,5-bis-(hydrocarbyldithio)-1,3,4-thiadiazoles and PA1 (e) 2,5-bis(hydrocarbyldithio)-1,3,4-thiadiazole.
Thus, the invention is further directed to silver protective lubricant compositions comprising organo-sulfur compounds in combination with the above-mentioned carboxylic acid-amine reaction products, as well as to a method for protecting silver engine parts which utilize such synergistic combinations.
2. Discussion of the Prior Art
Large numbers of medium speed diesel engines in the United States, as well as other countries, utilize silver-plated bearings. Thus, apart from providing stability against oxidation and protection against the formation of sludge and carbonaceous deposits, crankcase lubricating oils intended for use in medium speed diesel engines must also be formulated with specialized silver protecting agents in order that silver parts in the engine are not attacked either by the additives in the oil or by the dispersed neutralized decomposition products produced during extended engine operation. Such agents, often referred to as silver lubricity agents, protect against extreme pressure, wear and corrosion.
Although it is essential to include a silver lubricity agent in diesel oils intended for use in engines having silver parts, it is well known that such oils must exclude the zinc-containing anti-wear agents mentioned above, such as the zinc dihydrocarbyldithiophosphates, given the known propensity of the latter to damage the silver components of diesel engines. This is explained, for example, in U.S. Pat. No. 4,428,850 (column 1, lines 63-68).
The antagonism between zinc-containing wear inhibitors and the silver parts in diesel engines has been circumvented in the prior art by using alternative silver lubricity compounds, the most common of which are the chlorinated hydrocarbons such as shown in Sung, U.S. Pat. No. 4,171,269. However, while the chlorine compounds of the prior art have been shown to be effective in protecting the silver parts of diesel engines, the Occupational Safety and Health Administration in the United States and other public health agencies throughout the world have expressed concern over potential biological effects of chlorinated compounds. Therefore, an incentive exists to develop novel compositions effective in protecting the silver parts of medium speed diesel engines which overcome the problems or potential problems encountered with the zinc-containing and chlorine-containing wear inhibitors.
A related problem in obtaining silver protection in lubricant compositions is that overbased alkali and alkaline earth metal detergents, added to provide beneficial cleanliness properties to lubricant formulations, at the same time produce deleterious side effects on silver parts. Thus, while it is desirable to impart a high degree of alkalinity through the use of overbased detergents, such overbased materials tend to impair the silver protection characteristics of the oil, making it difficult to formulate a diesel lubricant composition which gives the desired level of cleanliness, yet at the same time protects the silver parts of the diesel engine. Therefore, a need exists for diesel lubricant additive compositions which not only protect the silver parts of the diesel engine, but also operate so as to render the lubricant composition tolerant to markedly higher levels of overbased detergents.
A number of patents are thought to be of relevance as background to the compositions and methods described in the present invention but do not address expressly, or even inherently, the problems described above. For example, Andress, U.S. Pat. No. 3,655,560, describes antioxidants and metal deactivators for fuel oils, lubricating oils and greases which are compounds selected from the group consisting of ketimines of aminoguanidine, aldimines of ketimines of aminoguanidine and aldimines of amides of aminoguanidine. This patent does not disclose or suggest the reaction product of a carboxylic acid with aminoguanidine as a silver lubricity agent in diesel lubricant formulations, as taught in the present invention.
Another patent relating to aminoguanidine in lubricant compositions is Frangatos, U.S. Pat. No. 4,295,982 which discloses products from aminoguanidines (or their salts), monocarboxylic acids and sulfur and their use as anti-rust and anti-corrosion additives. The compounds of this patent differ from those of the present invention insofar as sulfur is not used in the preparation of the compositions of the present invention. Moreover, Frangatos is not directed to the attainment of silver lubricity in diesel engines.
Knepper, et al., U.S. Pat. No. 4,595,523, is directed to a corrosion inhibiting composition comprising a triazole and an amine salt of an acid. While the patent states that "any amine which would form an acid salt which is soluble in an alcohol and inhibits corrosion may be used in the invention," there is no specific disclosure of carboxylic acid salts of aminoguanidine. Also, the invention of Knepper is clearly directed to a composition which is added to an alcohol fuel. Thus, the patent in no way relates to a lubricant composition, free of zinc compounds, which would be suitable for addition to a diesel engine lubricating composition used in a diesel engine having silver bearings.
Boehringer, et al., U.S. Pat. No. 3,749,702, describes metal deactivators useful as additives in lubricants and, more particularly, describes salts formed from amides prepared from benzoic acid or a substituted benzoic acid and aminoguanidine bicarbonate and an aliphatic or aromatic carboxylic acid. The present invention is not directed to the reaction product of a benzoic acid or its derivatives and aminoguanidine bicarbonate and is clearly distinguishable from Boeheringer, et al.
Biswell, U.S. Pat. No. 2,584,784, describes the higher aliphatic salts of 1-salicylalaminoguanidine as antioxidant additives. Representative acids which may be employed to form the salts in Biswell include oleic acid. Like the patents discussed above, Biswell is distinguishable from the present invention because it does not disclose the reaction product of carboxylic acids and aminoguanidine and is not directed to silver protection in diesel engine lubricants.
U.K. Patent Specification No. 1,440,129 discloses metal passivators used to reduce the corrosion of engine component materials such as copper and lead which include condensation products of salicylaldehyde with hydrazine derivatives and the C.sub.12 -C.sub.18 fatty acid salts of such condensation products such as the oleic acid salt of salicylalaminoguanidine, preferably the monooleic salt. The patent goes on to discuss useful load-carrying additives (extreme pressure agents) including zinc dihydrocarbyl dithiophosphates. Given the inclusion of zinc-containing wear agents in its discussion of wear inhibitors, the British Patent Specification is clearly not directed to lubricating compositions for diesel engines containing silver parts.
Lange, et al., U.S. Pat. No. 4,491,527, describes ester-heterocycle compositions useful as "lead paint" inhibitors in lubricants. In particular, at column 4, lines 34-51 (plus the accompanying drawings) the patentee describes the reaction of a substituted carboxylic acid (e.g., polybutylsuccinic acid) with an acyclic heterocycle precursor which cyclizes with the carboxylic acid group to form a heterocyclic compound. An illustrative acyclic heterocycle precursor which may react with an acid or an acid derivative group to form such heterocycles include aminoguanidine and salts thereof, semicarbazide, thiosemicarbazide, carbohydrazide and thiocarbohydrazide, as well as salts thereof such as aminoguanidine bicarbonate. Thus, the composition of Lange, et al. can include the 5-(polyalkenylsuccinic)-3-amino-1,2,4-triazole. The patent, however, is not specifically directed to a lubricant composition for use in diesel engines having silver parts. In fact, at column 12 of the patent, an illustrative lubricant composition of the invention is shown to include a zinc dialkylphosphorodithioate wear inhibitor which would be totally unacceptable in the present invention.
Sung, et al., U.S. Pat. No. 4,256,595, is directed to a diesel crankcase lubricant composition comprising a lubricating oil base and the reaction product of a hydrocarbyl succinic anhydride in which the hydrocarbyl radical has from 12 to 30 carbon atoms, and 5-aminotriazole. The background section of the patent states that it is known to employ a thiadiazole as a corrosion inhibitor for diesel crankcase lubricating oil. The patent, however, does not disclose or suggest a synergistic combination of 3-amino-1,2,4-triazole compounds and 1,3,4-thiadiazole compounds, as disclosed in the present invention.
Davis, U.S. Pat. No. 4,136,043, is directed to compositions useful for suppression of copper activity and "lead paint" deposition and lubricants. The compositions are produced by preparing a mixture of an oil soluble dispersant (preferably a substantially neutral or acidic carboxylic dispersant) and a dimercaptothiadiazole, preferably 2,5-dimercapto-1,3,4-thiadiazole. As stated at column 4, lines 24-39, the carboxylic dispersants encompass nitrogen bridged dispersants wherein the nitrogen group is derived from aliphatic, aromatic, heterocyclic and carbocyclic amines as well as substituted ureas, thioureas, hydrazines, guanidines, amidines, amides, thioamides, cyanamides and the like. Davis is not directed to the achievement of silver lubricity in lubricating compositions for diesel engines.